This Forum discusses the significant growth of international large-scale assessments (ILSAs) since the mid-1990s. Addey and Sellar's contribution outlines a framework of rationales for participating in ILSAs and examines the multiple localised meanings attached to ILSA participation. This framework is discussed under seven headings: (1) evidence for policy; (2) technical capacity building; (3) funding and aid; (4) international relations; (5) national politics; (6) economic rationales; and (7) curriculum and pedagogy. It shows how ILSAs can serve multiple purposes – a flexibility that has contributed to the rapid growth of the phenomenon. Steiner-Khamsi focuses on the local to understand why the global resonates and discusses how governments appropriate ILSAs for national agenda setting. Lingard examines the rationales of international organisations and the contribution of media coverage to the increasing significance of ILSAs. Finally, Verger theorises rationales for ILSA participation according to three frames for understanding global education policy: rationalism, neo-institutionalism and political economy approaches.